1. Field of the Invention
The present invention relates to a frequency spectrum analysis method and a frequency spectrum analyzer, and in particular to a frequency spectrum analysis method and a frequency spectrum analyzer in which frequency spectrum analysis is performed via software by using proper tested signals on a per communications system basis.
2. Description of the Related Art
FIG. 2 is a block diagram showing a conventional frequency spectrum analyzer. Two types of communications systems, Communications System A and Communications System B, are treated in this figure.
For Communications System A, tested signals S12A are input to a fast Fourier transformer 16. For Communications System B, tested signals S12B are input to the fast Fourier transformer 16.
Intermediate frequencies IFA, IFB and sampling frequencies SFA, SFB of Communications System A and Communications System B differ from each other; for example, the intermediate frequency IFA of Communications System A is 3.6 MHz and the sampling frequency SFA is 14.4 MHz while the intermediate frequency IFB of Communications System B is 100 kHz and the sampling frequency SFB is 400 kHz.
Communications System A and Communications System B use frequency spectrum resolutions different from each other to perform frequency spectrum analysis.
For example, the frequency spectrum resolution required of Communications System A is approximately 1800 Hz and the frequency spectrum resolution required of Communications System B is approximately 50 Hz. Sampling data count required by the fast Fourier transformer 16 is 8192 (2{circumflex over ( )}13) for both Communications System A and Communications System B.
Communications System A: 14.4 MHz÷8192=1757.8≈1760 Hz
Communications System B: 400 kHz÷8192=48.8≈50 Hz
The following describes a processing procedure to take when Communications System A or Communications System B is selected for frequency spectrum analysis.
In the case of frequency spectrum analysis in Communications System A, system selector switches SW2, SW3 are placed in the P1 position and an output frequency obtained through frequency synthesis of a radio frequency RF and a local frequency LO1A is input to a low-pass filter 11A composed of hardware and converted to an intermediate frequency IFA. The intermediate frequency IFA is input to an A/D converter 12A to obtain tested signals S12A as digital signals. The tested signals S12A are input to the fast Fourier transformer 16 to obtain frequency spectrum analysis results S16.
In the case of frequency spectrum analysis in Communications System B, system selector switches SW2, SW3 are placed in the P2 position and an output frequency obtained through frequency synthesis of a radio frequency RF and a local frequency LO1B is input to a low-pass filter 11B composed of hardware and converted to an intermediate frequency IFB. The intermediate frequency IFB is input to an A/D converter 12B to obtain tested signals S12B as digital signals. The tested signals S12B are input to the fast Fourier transformer 16 to obtain frequency spectrum analysis results S16.
The frequency spectrum analyzer has a problem that new hardware must be implemented for each communications system thus expanding the size of apparatus. In order to solve this problem, a configuration is proposed in which apparatus size is reduced by using the same hardware and realizing through software the difference in hardware design.
FIG. 3 is a block diagram showing a frequency spectrum analyzer with apparatus size reduced. Same as a conventional frequency spectrum analyzer, Two types of communications systems, Communications System A and Communications System B, are treated in this figure.
Apparatus size is reduced by sharing hardware between Communications System A and Communications System B. An intermediate frequency IF and a sampling frequency SF shall satisfy the test conditions of a conventional frequency spectrum analyzer and the IF and the SF shall be the higher of the IF frequencies and SF frequencies of Communications System A and Communications System B, respectively.
For both Communications System A and Communications System B, tested signals S12 are input to the fast Fourier transformer 16. Required frequency spectrum analysis resolution is obtained by changing the sampling data count at fast Fourier transform depending on the communications system employed.
Thus the intermediate frequency IF is 3.6 MHz and the sampling frequency SF is 14.4 MHz. Same as a conventional frequency spectrum analyzer, the frequency spectrum resolution required of Communications System A is approximately 1800 Hz and the frequency spectrum resolution required of Communications System B is approximately 50 Hz. Sampling data count required by the fast Fourier transformer 16 is 8192 (2{circumflex over ( )}13) for Communications System A and 262144 (2{circumflex over ( )}18) for Communications System B.
Communications System A: 14.4 MHz÷8192=1757.8≈1760 Hz
Communications System B: 14.4 MHz÷262144=54.9≈55 Hz
The following describes a processing procedure to take when Communications System A or Communications System B is selected for frequency spectrum analysis.
In the case of frequency spectrum analysis in Communications System A, an output frequency obtained through frequency synthesis of a radio frequency RF and a local frequency LO is input to a low-pass filter 11 composed of hardware and converted to an intermediate frequency IF. The intermediate frequency IF is input to an A/D converter 12 to obtain tested signals S12 as digital signals. The tested signals S12 are input to the fast Fourier transformer 16 to obtain frequency spectrum analysis results S16.
The frequency spectrum analysis in Communications System B is the same as that in Communications System A. However, the sampling data count required by the fast Fourier transformer 16 is a huge 262144. This resents problems that the processing time is extremely long and memory used for operation such as fast Fourier transform is large.
A conventional frequency spectrum analyzer has a problem that the apparatus size is large and a frequency spectrum analyzer with apparatus size reduced has problems that memory usage is large and frequency spectrum analysis takes huge processing time.
For a frequency spectrum analyzer with apparatus size reduced, reduced sampling data count required by the fast Fourier transformer in Communications System B would shorten the processing time and reduce memory usage.
The object of the invention is to provide a frequency spectrum analyzer wherein apparatus size is reduced, processing time is shortened, and memory usage is reduced while the conventional frequency spectrum analysis performance is retained, by adding a signal processor in software which provides an intermediate frequency and a sampling frequency equivalent to those of a conventional frequency spectrum analyzer for each communications system, based on a frequency spectrum analyzer with apparatus size reduced.
The invention solves the aforementioned problems via the following frequency spectrum analysis methods and frequency spectrum analyzers:
1. A frequency spectrum method comprising the steps of:
converting each radio frequency of a plurality of communications systems to tested signals as digital signals via single A/D conversion means,
inputting said one A/D-converted tested signal to Fourier transform means for frequency spectrum analysis,
converting said other A/D-converted tested signal and a local frequency via a tested signal converter,
filtering the converted tested signals to convert them to tested signals containing necessary signal components, and
decimating the filtered tested signals and performing frequency spectrum analysis on the decimated tested signals via the Fourier transform means.
2. A frequency spectrum method comprising the steps of:
synthesizing each of the radio frequencies with local frequencies and filtering the frequency-synthesized tested signals to convert them to tested signals containing necessary signal components, and performing A/D conversion on the tested signals to obtain the digital signals.
3. A frequency spectrum analyzer for performing frequency spectrum analysis comprising:
a tested signal converter for inputting tested signals and outputting converted tested signals,
a low-pass filter for inputting the converted tested signals and outputting filtered tested signals,
a sampling frequency converter for inputting filtered tested signals and outputting tested signals,
system selector switches for switching between communications systems, and
a fast Fourier transformer for inputting tested signals and outputting frequency spectrum analysis results, characterized in that frequency spectrum is analyzed via software by using proper tested signals for each communications system.
4. A frequency spectrum analyzer, characterized in that the tested signal converter performs frequency synthesis of tested signals and local frequencies to convert the tested signals to the tested signals in a proper frequency band.
5. A frequency spectrum analyzer, characterized in that the system selector switches make switching so that one tested signal is input to the fast Fourier transformer and the other tested signal is converted by the tested signal converter, low-pass filter and sampling frequency converter, and the converted signal is input to the fast Fourier transformer.
6. A frequency spectrum analyzer for converting each of radio frequencies of communications systems having different frequencies to digital signals via a single A/D converter and performing frequency spectrum analysis on the digital signals via a frequency spectrum analysis section consisting of a single fast Fourier transformer, the frequency spectrum analysis section comprising:
a tested signal converter for inputting tested signals and outputting converted tested signals,
a low-pass filter for inputting the converted tested signals and outputting filtered tested signals,
a sampling frequency converter for inputting filtered tested signals and outputting tested signals,
system selector switches for switching between communications systems, and
a fast Fourier transformer for performing frequency spectrum analysis on the selectively input tested signals and outputting frequency spectrum results, characterized in that frequency spectrum is analyzed via software by using proper tested signals for each communications system.
7. A frequency spectrum analyzer, characterized in that the single A/D converter comprises:
a low-pass filter for converting to intermediate signals the frequency obtained by synthesizing each of the radio frequencies and a first local frequency and
an A/D converter for A/D-converting the intermediate frequency.
8. A frequency spectrum analyzer, characterized in that the tested signal converter performs frequency synthesis of tested signals and a second local frequency to convert the tested signals to the tested signals in a proper frequency band.
9. A frequency spectrum analyzer, characterized in that the system selector switches make switching so that one digitally converted signal is input to the fast Fourier transformer and the other digitally converted signal is converted by the tested signal converter, low-pass filter and sampling frequency converter, and the converted signal is input to the fast Fourier transformer.